For real gases, how does a change in pressure affect the ratio of PV to nRT?

1 Answer
Jul 14, 2017

It depends on the gas. The ratio of #PV# to #nRT# is the compressibility factor #Z#:

#Z = (PV)/(nRT)#

  • When #Z > 1#, the molar volume of the gas is larger than predicted by the ideal gas law, so the gas's repulsive intermolecular forces dominate.

  • When #Z < 1#, the molar volume of the gas is smaller than predicted by the ideal gas law, so the gas's attractive intermolecular forces dominate.

  • When #Z = 1#, the gas is ideal.

In principle, higher pressures (and lower temperatures) should make the gas behave more like a real gas (interacting, "sticky" particles).

But higher pressures alone don't give rise to a clear relationship with #Z#.

http://www.chemguide.co.uk/

You can see that at higher temperatures, the curve for #"N"_2# converges upon #Z = 1# across a large range of pressures, demonstrating that very high temperatures give rise to an ideal gas. Having low pressures as well makes it easier to accomplish that feat.